A typical KHP system is described in U.S. Pat. No. 4,613,279 the entire contents of which are incorporated herein by reference. Typical KHP systems employ one or more turbines anchored to a river bottom each of which include an external rotor that rotates in response to water flowing there past that is coupled, via a rotating shaft seal, to a nacelle or the body of the turbine. The nacelle desirably is a watertight enclosure of the turbine in which machinery comprising various electrical and mechanical components are contained. Rotation of the rotor causes the electrical and mechanical components to generate power and cable connections are needed so that the generated power can be transmitted from the turbine onto the power grid or other load and the electrical signals can be sent to or received from the turbine at an onshore control facility.
The rotating shaft seal may be less than perfectly watertight in KHP system turbines, and water can leak into the closed nacelle portion of the turbine which can cause problems. In one embodiment this problem is overcome by having the electrical cables connecting the turbine to the station sealed to the nacelle and at their far ends as well to prevent internal air within the nacelle from venting along the cables. In another embodiment use is made of the cable's ability of conducting gases, either through the spaces between wires within the cable, or via a separate gas channel, to link a pressure source to the interior of the nacelle to thereby maintain a positive pressure in the nacelle in order to counteract the inward pressure of the surrounding water.
The specific problem for underwater turbines is the need to prevent water from entering the sealed nacelle, such as possible through the dynamic (rotating) shaft seal of the turbine, through the connection to a supporting pylon, or any other joint or seam (static seals) in the nacelle. Keeping air within the nacelle or by providing air or another fluid, such as dry nitrogen, under pressure along the cable, a positive pressure can be created and maintained within the nacelle so that water can be kept out of both the nacelle and the cable itself.
Furthermore, since the nacelle is underwater, water pressure is acting on the exterior of the nacelle and depending on the depth of the nacelle the water pressure may be significant. Exposure to significant water pressure may cause water to leak through the seals of the nacelle. For this reason, it can be desirable to keep the interior of the nacelle at an equal or even higher pressure than the exterior water pressure, thus creating a zero net pressure differential of an overall positive pressure within the nacelle.
A positive pressure or atmosphere can be created and maintained within the nacelle through the use of a novel pressurized cable system that includes particular cable end seals, and for creating a positive pressure uses an open passageway that extends along the length of the power and/or data cables. This is accomplished by using an existing or designing a purpose-built cable that can provide art open pathway to send positive pressure along the length of the cable to the nacelle, encase the necessary power and electrical conduits, and yet be accessed at each of the distal and proximal ends in such way that electric control signals and the generated power can be accessed while maintaining suitable positive gas pressure along the length of the cable even when bent. Further, water ingress can be prevented by simply preventing air from venting through cables connecting under water power turbine to onshore control facility by sealing the cable ends.
This allows the following benefits: not allowing the air to vent from within the nacelle and/or maintaining a positive pressure within the nacelle prevents ingress of water at the turbine nacelle end and the gas pressure in the cable and nacelle can be monitored and controlled from the proximal end. Furthermore, in the event that the cable jacket is punctured, the effect thereof can be minimized, since there is a positive pressure throughout the length of the cable. Additionally, changes in the sealing status of the nacelle and cable can be detected via changes in the flow rate of the pressurizing medium.